This invention relates to suspension systems for tracked vehicles, and, more specifically, to a slide rail system for a snowmobile.
Generally, suspension systems are very heavy and bulky due to their complexity and the number of parts required. As illustrated in FIGS. 1 and 2, most suspension systems require a pair of elongated slide rails 1 that are curved at their forward end 2 to follow an endless track 3. Front and rear suspension arms 4, 5 link the slide rails 1 and the chassis 6 of the snowmobile 7 together. The front and rear suspension arms 4, 5, together along with the chassis 6 and the slide rails 1, form a parallelogram structure.
One aspect that all prior art suspension systems have in common is the shape of the slide rails 1. Slide rails 1 have generally been structured to include a flat surface 8 toward the rear end of the slide rail 1, which slides along an endless track parallel with the ground. The forward end 2 of the slide rails 1 curves or angles towards the chassis 6 to create an angle of attack  of the track 3. Another aspect that is common to the prior art slide rails is an unsupported front portion of the track between the front drive axle and the forward end 2 of the slide rails.
The distance needed to ensure the minimum amount of traction between the snowmobile track 3 and the ground determines the minimum length of the rear flat surface 8.
Several suspension designs appear in the prior art, a few of which are described briefly below.
U.S. Pat. No. 5,860,486, incorporated herein by reference, describes a suspension system comprising a single, generally centrally mounted structure in a middle portion of the rear suspension system. The suspension system comprises a pair of inclined primary suspension numbers and a pair of inclined primary oscillating arms pivotally connected to a pair of longitudinal slide rails. U.S. Pat. No. 5,860,486 describes one central suspension arm. Shock absorbers provide for a second attachment between the slide rails and the chassis. Specifically, because of this design, the slide rails do not extend all the way to the forward drive axle, thus creating a space where the track fails to contact the slide rails, which adversely effects snowmobile performance in soft snow.
U.S. Pat. No. 5,033,572, incorporated herein by reference, describes a suspension system having a pair of slide rails, which incorporate two angles of attack. One of the angles of attack favors trail riding while the other provides necessary traction in deeper snow.
U.S. Pat. No. 5,904,216, incorporated herein by reference, describes a suspension system that provides a compact assembly and yet permits the use of a single cushioning unit that extends horizontally within the frame to provide large suspension travel in a relatively small area.
While these designs offer certain advantages, they also suffer from certain drawbacks, which result from reliance on the traditional slide rail as the primary element of the suspension. One specific drawback of conventional slide rails system is the need of front and rear suspension arms that attach the slide rails to the chassis. The need of two suspension arms renders the conventional suspension systems heavy and bulky. A second drawback is the unsupported front portion of the track between the front drive axle and the forward end of the slide rails. This unsupported portion of the track tends to cave inwards due to the pressure of the snow thus creating a lump of snow which the slide rails must travel over or push through, preventing the track from riding on the top surface of the snow.
There is a need for a new and improved slide rails system that offers an improved construction to avoid, or at least lessen, the effect of the drawbacks described above.
It is an object of the present invention to provide a new slide rail system with improved characteristics that will help decrease the weight and cost of the entire suspension system, provide greater support for the track, and create an improved angle of attack for the track.
It is another object of the present invention to provide a slide rail system, which includes a pair of parallel elongated front slide rails attached together with a series of transverse bars pivotally attached to a second pair of parallel rear slide rails attached together with a series of transverse bars. The forward end portions on the front slide rails are pivotally attached to the chassis of a snowmobile near the front drive sprocket thereby providing support for the entire portion of the track engaging with the terrain over which the vehicle is driven.
Still another object of the present invention is to provide a slide rail system where the front slide rails are attached to the chassis through a linkage member.
Still another object of the present invention is to provide a slide rail system where the front slide rails are directly attached to the front drive axle of a snowmobile.
Another object of the present invention is to provide a slide rail system where the ratio between the length of the front slide rails and the rear slide rails is between 50% and 100%.
Yet another object of the present invention is to provide a slide rail system where the pivot point between the front and rear slide rails is situated a predetermined distance from the drive axle of the snowmobile.
It is still another object of the present invention to provide a slide rail system where the pivot point between the front slide rails and the chassis is a predetermined distance from the front drive axle of the snowmobile.
It is yet another object of the present invention to provide a suspension system where the slide rails include a pair of front and rear slide rails. The front and rear slide rails are pivotally connected to one another. The front slide rails are also adapted to be pivotally connected to the chassis near the front drive axle. The suspension system includes at least one suspension arm attaching one of the rear slide rails and the front slide rails to the chassis and one shock assembly attaching one of the front slide rails and the rear slide rails to the chassis of the snowmobile.
According to another aspect of the present invention, a snowmobile is provided that includes a chassis. An engine is disposed on the chassis. A steering column is attached to at least one ski for steering the snowmobile over the snow. An endless track is disposed under the chassis and is operatively connected to the engine for propelling the snowmobile. The snowmobile includes a slide rail system, which includes a pair of parallel elongated front slide rails attached together with at least one transverse bar pivotally attached to a second pair of parallel rear slide rails also attached together with transverse bars. The front-end portions of the front slide rails are pivotally attached to one of the chassis of a snowmobile near the front drive axle or directly to the front drive axle.
Another object of the present invention is to provide a snowmobile with a suspension system that includes a pair of front and rear slide rails which pivot with respect to one another. The suspension system includes at least one suspension arm attaching one of the front slide rails and the rear slide rails to the chassis and one shock assembly attaching one of the front slide rails and the rear slide rails to the chassis of the snowmobile.
Yet another object of the present invention is to provide the slide rail system with a mechanism that will prevent the rotation of the rear suspension arm such that the weight transfer of the vehicle will be controllable.
Still another object of the present invention is to provide a snowmobile with a suspension system in which the ratio of the length of the endless track to the length of the rear slide rails is a predetermined number.
It is still another object of the present invention to provide a snowmobile with a suspension system in which the ratio of the length of the endless track to the length of the front slide rails is a predetermined number.
The foregoing objects are not meant to limit the scope of the present invention. To the contrary, still other objects of the present invention will become apparent from the description that follows.